[abecedarius]

I wonder if you could "blow a hole" through the atmosphere (very briefly) and send your real payload after. Sounds absurd, but then so did Orion. I expect you could only manage a transient rarefication behind a rapidly-slowing "rabbit", alas.

[DanielBMarkham]

There's definitely some interesting math going on. For example, max aerodynamic pressure happens immediately, on launch, with each additional millisecond decreasing stress on the payload.

At high enough speeds, does the atmosphere supercavitate? Could you use a double-shot, with the first projectile basically ablating away and creating a "wake" for the second to fly through?

[credit_guy]

I think the aerospike concept is related to this solution.

https://en.m.wikipedia.org/wiki/Drag-reducing_aerospike

[abecedarius]

Interesting. The "air spike" referenced there is like another idea I was wondering about: cross a bunch of laser beams ahead of the bullet, from a spread-out set of ground-based lasers. Like laser launch, but for rarefying the air in front instead of for powering a rocket.